This invention relates to a multiple valve internal combustion engine and more particularly to an improved combustion chamber and valve arrangement for such an engine.
It is generally recognized that the breathing capabilities of an internal combustion engine can be improved by using plural valves rather than individual valves of a large diameter. The use of four valves per cylinder has been generally regarded as the practical limit. Such arrangements employ two intake valves and two exhaust valves. The reason why four valves per cylinder has been deemed to be the practical limit is the trade off between breathing capacity and combustion chamber configuration and volume. That is, if engines are employed that utilize more than four valves per cylinder, the combustion chamber surface area becomes quite large and the clearance volume also increases. As a result, it is difficult to provide a high compression ratio, which is also necessary in order to achieve maximum output for the displacement of the engine.
Recently, a combustion chamber configuration has been proposed that will permit the use of five valves (three intake and two exhaust) for each combustion chamber of the engine without adversely effecting the combustion chamber surface area or reducing the compression ratio. Such a valve arrangement is shown in U.S. Pat. No. 4,660,529, issued Apr. 28, 1987 in the name of Masaaki Yoshikawa, entitled "Four-Cycle Engine" and assigned to the assignee of this application. Although the valve placement disclosed in that patent does permit the use of five valves per cylinder without adversely effecting the compression ratio or the combustion chamber surface volume, it has certain difficulties.
The difficulties of the prior art construction may be best understood by reference to FIGS. 1 through 3 which are, respectively, a cross sectional view taken through a horizontal plane looking generally in the direction of the arrow 1 in FIG. 2, a cross sectional view taken along the line 2--2 in FIG. 1 and a side elevational view taken generally along a plane shown by the line 3--3 in FIG. 1, with portions removed to show the valve orientation.
Only a single cylinder of the engine is depicted because it is believed that those skilled in this art will understand how the construction is applied to multiple cylinder engines. The engine includes a cylinder block 11 having a cylinder bore 12 which is, conventionally, of the right circular configuration, although other configurations may be employed. A cylinder head 13 is affixed to the cylinder block 11 and closes the upper end of the cylinder bore 12, as is well known. A combustion chamber, indicated generally by the reference numeral 14 is formed by the cylinder bore 12, the head of the piston (not shown) and a recess 15 formed in the cylinder head 13. This recess is defined by a surface 16 that is somewhat smaller in size than the cylinder bore 12 so as to provide some squish area that extends around this recess surface 16
The cylinder head surface 16 is formed with a central intake port 17 and a pair of side intake ports 18 and 19 which are generally circular in configuration. A center intake valve 21 cooperates with the center intake port 17 so as to control the flow through this intake port. A pair of side intake valves 22 and 23 cooperate with the side intake ports 18 and 19 so as to control the flow through these ports.
In accordance with the construction described in the aforenoted U.S. Pat. No. 4,660,529, the intake valves 21, 22 and 23 are supported so that the axes of reciprocation defined by the stems of these valves are disposed at certain angular relationships. However, the axes of reciprocation all lie in planes that are parallel to each other and parallel to a plane containing the axis of the cylinder bore 12. Generally, the center intake valve 21 has its valve stem reciprocating in this latter mentioned plane. The reason for this orientation is so that the valves can all be operated conveniently by the lobes of a single camshaft. To that end, the axes of reciprocation all intersect on a line that is coincident with the axis of rotation of this camshaft.
As a result of this configuration, the areas 24 of the cylinder head formed between the intake port 1 and the intake ports 18 and 19 has a somewhat irregular configuration. This configuration may be understood by reference to the figures and is necessary in order to permit the valves to operate conveniently in the aforedescribed manner.
A pair of exhaust ports 25 are positioned on the opposite side of a plane passing through the cylinder bore axis and perpendicular to the plane containing the axis of reciprocation of the valve 21. As mentioned in the aforenoted United States Letters Patent, the intake ports 18 and 19 extend slightly over onto the other side of this plane. A pair of exhaust valves 27 and 28 control the flow through the exhaust ports 25 and 26. The exhaust valves 27 and 28 reciprocate along lines that lie within a common plane and in planes that are parallel to each other and parallel to the plane containing the axis of reciprocation of the intake valve 21. As a result, the valves 27 and 28 may be operated by a single exhaust camshaft that rotates about an axis that is parallel to the axis of rotation of the intake camshaft.
A spark plug 29 is positioned generally centrally in the combustion chamber 14 and lies generally on the plane containing the axis of reciprocation of the intake valve 21 and on the cylinder bore axis.
As aforenoted, the described combustion chamber, although compact and permitting good breathing, does have some disadvantages in that there is some masking of the valves and the combustion chamber surface is not smooth.
It is, therefore, a principal object of this invention to provide an improved combustion chamber and valve arrangement for a multiple valve internal combustion engine.
It is a further object of this invention to provide an improved five valve per cylinder arrangement for an internal combustion engine that permits the use of a high compression ratio, good breathing, and which provides also a smooth combustion chamber.
It is a further object of this invention to provide an improved arrangement for operating and locating the valves in a five valve per cylinder engine.
It has been found that the aforenoted results can be achieved by skewing the axes of reciprocation of the side intake valves so that they do not reciprocate in planes that are parallel to the plane of reciprocation of the center intake valve. In order to accomplish this and still drive the arrangement with a single camshaft, it is, therefore, desirable to provide angularly disposed cam lobes that operate these side valves. However, the formation of such angularly disposed lobes gives rise to certain manufacturing problems.
It is, therefore, a still further object of this invention to provide an arrangement for forming a camshaft that is adapted to operate valves that are angularly disposed and wherein a tapered cam lobe may be conveniently formed.